Trap Catches Identified to July 12
Trap catches for the week of July 05-12 remain low. However, 1 Damson-Hope aphid was recovered from Gully, MN. This aphid has been reported as being ~1/2 as efficient as Green Peach Aphid, meaning it could be a major player in spreading PVY if we see numbers this season.
Data from other researchers continues to highlight the value of early application of crop oils (e.g. Aphoil, JMS Stylet oil). Researchers in New Brunswick have also reported additional value in adding either lambda-cyhalothrin insecticides (e.g. Warrior II, Silencer, Grizzly, etc) or the insecticide, Beleaf to oil applications. All products should be suitable for tank mixing with fungicides (but remember to always check the label! a jar test may also be useful if you have concerns). No other insecticides tested were found to provide additional efficacy.
While numbers are low to this point, aphids are flying and, if you haven't started, it's time to start...
As always, keep on scouting!
Scouting for aphids in potatoes:
- Select leaves from the lower to mid canopy. Start at the edge of the field.
- Lower, older leaves will have more established colonies and aphids prefer the balance of nutrients found here; aphids are rarely found on leaves in the upper canopy.
- Avoid leaves on the ground or in contact with the soil.
- In seed potatoes there is only a threshold for PLRV (10 aphids/100 leaves), reactive application of insecticides an effective control for PVY.
- The use of feeding suppressing insecticides, such as pymetrozine (Fulfill®) or flonicamid (Beleaf®) and refined crop oils, such as Aphoil and JMS Stylet Oil, at or prior to field colonization by aphids may reduce the transmission of PVY within fields. Some other insecticides, such as clothianidin (Belay®), imidacloprid (Admire Pro® or Provado®), and spirotetramat (Movento®), have also been demonstrated to reduce the transmission of PVY.
- In table stock potatoes, a treatment threshold of 30 aphids /100 leaves should deter yield loss due to aphid feeding.
The PVY Risk Index Index
Not all species of aphid are equally efficient at transmitting PVY, some are better than others (green peach being the most efficient vector of PVY). So, the total number of aphids in a trap don't necessarily reflect just how much vector pressure there is at that location. The PVY Vector Risk Index compares aphid numbers, incorporating their relative vector efficiency compared to the Queen of PVY vectors (green peach aphid!). Using averaged reference comparisons from the literature, we multiply the number of each aphid species captured by its efficiency compared to Green Peach Aphid to more accurately depict risk posed by the species being trapped. We then sum the totals. The PVY-VRI values are presented on the tables below but also on maps comparing current cumulative risk to the total risk from the sample sites of last year (to compare with your local winter grow out results).